Bob Plunkett, Wed, 10 Mar 2010 10:22:30 PST

Then we wind up so much torque on the new supercharged engine in a revamped S4 sports sedan by Audi of Germany.

Next, our left foot eases off the brake, the right one tromps the go-pedal as both hands take hold of a sporty steering wheel: So we're off on a hair-raising romp over a curlicue course to demonstrate that a four-door sedan designed to cart all in the family can also play it hard and fast on the fun side of four-wheeling performance.

Weight-saving aluminum components make the suspension, tuned and tweaked for precise and predictable German road manners, feel light and lively, while Audi's Quattro system for grip on every tire sets up a curve-craving machine which seems to defy the laws of physics.

Plying the manual stick, we run the tachometer's needle up to red in each lower gear to maximize momentum as rubber bites into soft asphalt to hold a tight line around so many snaky corners.

Each curve comes quickly, one followed immediately by another but in the opposite direction, then the next opposing again and still another and yet another. Switch, switch, switch, we swing back and forth through each turn with the car taking a taut line and all tires clawing for grip.

The challenge comes from keeping those four wheels locked on the narrow road as inertial forces try to pry us off at each turn and fling the vehicle into thin air.

But the new S4 quickly demonstrates it can master such torture on pavement in a stable and confident manner and we find ourselves zipping the Cachagua course, flitting fast through each turn, pushing the G-force to max tolerances as we soar over the route.

And on a straightaway -- the multi-lane 101 running south from Salinas - the super sedan acts like it's the swiftest car on the planet.

It's incredibly quick -- under five seconds from stand-still to 60 mph and on to 106 mph for the quarter-mile split in only 13 seconds, with the top speed electronically capped at 155 mph.

Even at such a furious pace the S4 runs with bedrock stability as if rooted to the road with not a twitch of doubt that it can handle uber-speeds of an autobahn racer.

So much strength, such corner-cutting agility and the ability to virtually fly across the land.

All of these attributes apply to the 2010 S4 3.0 TFSI, yet Audi's new muscle car camouflages well to all but educated eyes, as it resembles a conventional four-door sedan, rather roly-poly round yet svelte in shape for all body parts, with the five-seat cockpit -- lined in leather and studded with power-everything tools -- of a refined luxury vehicle.

Theme for S4's exterior design is a muscular fluidity of lines drawn in rectangular format but topped by an arching canopy over the cabin with narrow windows and side pillars muted to create the impression of a sleek coupe.

A discreet spoiler lips over the trailing edge of the trunk, while in the lower fascia there are two oval exhaust pipes on each corner which subtly convey the message that this is indeed a car of contentious strength.

The suspension, intensive in lightweight aluminum components, is independent at all four posts.

Steering, using a rack and pinion arrangement, is quick and Servotronic power assistance is standard, varying the degree of boost according to road speed.

Brakes, with a big disc at each wheel, rely on electronic and computerized links to tame the tires. Anti-lock brake (ABS) controls are standard, along with electronic brake distribution (EBD) plus Audi's electronic stabilization program (ESP) that checks lateral slippage and skidding.

S4 also comes with Audi's Quattro all-wheel-drive system. Using a self-locking center differential with 40/60 rear-biased torque split, the smart mechanism automatically shifts the majority of all engine torque to whichever wheels, front or rear, attain the best bite of traction.

The new optional Sports Rear Differential for S4 enhances wheel control and mimics the handling traits of a rear-wheel-drive (RWD) sportster.